826 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



this result from emotional excitement, which keeps repose at bay, or from a 

 voluntary determination to keep the intellect in activity. This is a very com- 

 mon occurrence among industrious students, who, with a laudable desire for 

 distinction, allow themselves less than the needed quantum of repose. Head- 

 ache, tension, heat, throbbing, and various other unpleasant sensations in the 

 head, give warning that the brain is being overtasked ; and if this warning be 

 not taken, sleep, which it was at first difficult to resist, becomes even more 

 difficult to obtain ; a state of general restlessness and feverish excitement are 

 induced ; and if, in spite of this, the effort be continued, serious consequences, 

 in the form of cerebral inflammation, apoplexy, paralysis, fever, insanity, or 

 loss of mental power, more or less complete, are nearly certain to be induced. 

 Some individuals can sustain such an effort much longer than others, but it is a 

 great mistake to suppose that they are not equally injured by it; in fact, being 

 possessed with the belief that they are not suffering from the exertion, they fre- 

 quently protract it until a sudden and complete prostration gives a fearful 

 demonstration of the cumulative effects of the injurious course in which they 

 have been persevering. Those, consequently, who are earlier forced to give 

 way, are frequently capable of accomplishing more in the end. In regard to 

 the degree of protraction of sleep which is consistent with a healthy state of 

 the system in other respects, it is difficult to speak with certainty. Of the 

 numerous well-authenticated instances on record, 1 in which sleep has been con- 

 tinuously prolonged for many days or even weeks, it is enough here to state that 

 they cannot be regarded as examples of natural sleep ; the state of such persons 

 being more closely allied to hysteric coma. An unusual tendency to ordinary 

 sleep generally indicates a congested state of the brain, tending to apoplexy ; 

 and it has been stated that apoplexy has been actually induced by the experi- 

 mental attempt to ascertain how large a proportion of the diurnal cycle might 

 be spent in sleep. Thus, on either side, inattention to the dictates of Nature, 

 in respect to the amount of sleep required for the renovation of the system, 

 becomes a source of disease, and should therefore be carefully avoided. 3 



1 Such, for example, as that of Samuel Chilton ("Phil. Trans.," 1694), and that of 

 Mary Lyall ("Trans, of Roy. Soc. of Edinb.," 1818). 



2 On Mesmerism. It appears to the Author that the time has now come, when a tolerably 

 definite opinion may be formed regarding a large number of the phenomena commonly 

 included under the term "Mesmerism." Notwithstanding the exposures of various pre- 

 tenders, which have taken place from time to time, there remains a considerable mass of 

 phenomena, which cannot be so readily disposed of, and which appear to him to have as 

 just a title to the attention of the scientific Physiologist as that which is possessed by any 

 other class of well ascertained facts. 



Passing over, for the present, the inquiry into the manner in which these effects may be 

 induced, the Author may briefly enumerate the principal phenomena which he regards as 

 having been veritably presented in a sufficient number of instances to entitle them to be 

 considered as genuine and regular manifestations of the peculiar bodily and mental condi- 

 tion under discussion : 



1. A state of complete Coma or perfect insensibility, analogous in its mode of access and 

 departure to that which is known as the " Hysteric Coma," and (like it) usually distinguish- 

 able from the Coma of Cerebral oppression by a 'constant twinkling movement of the eye- 

 lids. In this condition, severe surgical operations may be performed, without any con- 

 sciousness on the part of the patient ; and it is not unfrequently found that the state of 

 torpor extends from the Cerebrum and Sensory Ganglia to the Medulla Oblongata, so that 

 the respiratory movements become seriously interfered with, and a state of partial asphyxia 

 supervenes. 



2. A state of Somnambulism or Sleep-waking, which may present all the varieties of the 

 natural Somnambulism, from a very limited awakening of the mental powers, to the state 

 of complete Double Consciousness, in which the individual manifests all the ordinary powers 

 of his mind, but remembers nothing of what has passed when restored to his natural 

 waking state; This state of Somnambulism, in the form which it commonly takes, is 

 characterized by the facility with which the thoughts are directed into any channel which 

 the observer may desire, by the principle of "suggestion;" and by the want of power, on 



